George A. Romero could never have guessed what he was letting loose in 1968 when he directed the original Night of the Living Dead, the opening chapter of a wildly influential series that has run for more than 40 years. Other directors have followed up with comic zombies (Shaun of the Dead), romantic zombies (Warm Bodies) and now, in Marc Forster's World War Z, the first zombie film that could conceivably be nominated for an Oscar.

Not that Forster is more serious than Romero: on the contrary, he's the model of a respectable hack who has made everything from a Bond movie (Quantum of Solace) to an arty Will Ferrell comedy (Stranger than Fiction) without revealing much personality of his own. He lacks Romero's taste for blood and guts, staging his ghastly set-pieces with professional discretion. Equally, he shows no trace of Romero's subversive bent, though the script by several hands aims to tackle political issues - terrorism, the plight of refugees and so forth - in fantasy terms.

A dour techno-thriller, World War Z originated as a best-selling 2006 novel by Max Brooks - a deadpan stunt that bills itself as an ''oral history of the zombie war'', leaping from one narrator to another. By contrast, the film has a single hero, Gerry Lane, a retired UN investigator played by Brad Pitt with a calculated blend of gravitas and boyishness (the bags under his eyes suggest maturity, while his scruffy beard and long hair recall his younger days as a '90s hipster).

The zombie plague menacing Brad Pitt in World War Z seems allegorical.

Known as a good man in a crisis, Gerry proves his mettle by shielding his wife (Mireille Enos) and daughters from fast-moving zombies on the streets of Philadelphia, in a local outbreak of a plague running rampant across the globe. After he and his family find shelter on a UN aircraft carrier, he's drafted to hunt down the source of the infection.

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Gerry is reluctant to accept the mission, and does so only when he's warned that his loved ones will otherwise be kicked out of the safety zone. This scenario hints at a cynical view of authority carried over from Brooks' book, as if the plague reinforced the existing gap between the wretched mass of humanity and the privileged few.

Yet Hollywood convention creates a similar hierarchy - encouraging us to sympathise first with Gerry, second with his family, and hardly at all with disposable minor characters, let alone the zombies themselves. It's the same strategy used in Juan Antonio Bayona's The Impossible, in which Ewan McGregor, as a British victim of the 2004 Indian Ocean tsunami, was made to seem far more important than 1000 dying extras. Part of what made The Impossible so unpleasant was Bayona's willingness to treat a recent catastrophe as an excuse to show off his technique.

Working in a purportedly escapist genre, Forster has even fewer scruples: even as he asks us to associate the zombie crisis with real-world horrors, his overhead tracking shots and jittery Bourne-style chase sequences (in 3D) serve as nudging reminders that a zombie movie is supposed to be grisly fun.

What power the film has is concentrated in a couple of scenes. In the first, hordes of zombies swarm like ants over a wall around Jerusalem; in the second, passengers on a plane abruptly turn on one another as infection spreads. In both cases, horror is prompted by the spectacle of bodies reduced to rubbish - and by the sense that Forster might be offering an allegorical vision of the planet's future, as the population rises while resources decline.

In such a future, would the distinction between heroes and monsters really apply? Romero regularly asks us to ponder similar questions, but Forster isn't so concerned. Luckily, Pitt is on hand to save the day, delivering the closing moment of uplift required of mainstream entertainment.